1. Field of the Invention
This invention relates to an artificial intervertebral disk implant. More particularly, the present invention relates to cylindrical and rectangular disk implants which are expandable in the middle and can be used alone or in various combinations for the purpose of spinal fusion.
2. Description of the Related Art
The spine is a flexible structure comprised of thirty-three vertebrae. The vertebrae are separated and cushioned from each other by fiber cartilage in structures called intervertebral disks. If the spine is injured or becomes diseased, these disks are surgically removed. Such disk injuries can happen in the neck, in the thoracic region and in the lumbar region. The more frequent injuries are in the lower lumbar and in the lower cervical regions.
Treatment of herniated disk in the neck and in the lumbar region continues to be a challenging field of medicine. The classical treatment for a ruptured disk continues to be removal of the disk which is normally needed between the vertebrae. In the process, a defect is made which continues to bother the patients throughout the rest of their life. One additional procedure previously attempted is to replace the disk space with a bone graft, thus, bringing about a spinal fusion, i.e. a fusion of the two vertebrae thus eliminating the empty space between the vertebrae.
Theoretically, this is a satisfactory procedure, though not ideal because the replaced bone does not have any of the functions of the cartilage tissue, i.e. no cushioning effect. This procedure, however, is technically demanding and has medical complications because of several physiological factors. First of all, the bone plug used to pack the disk space does not conform to the shape of the disk because the disk bulges maximally in the center. The disk space is wider in the middle and narrow at its anterior and posterior ends. It is impossible to insert a bone plug having its maximum width at the center because it cannot be inserted through the mouth of the disk space. For this reason, the various bone plugs have only four point contacts, i.e. at the front and back part of the disk space. Secondly, if the bone pieces do not fuse within a minimum period of time, they dissolve, become thinner and many eventually extrude out of the disk space, causing pressure on the nerve roots.
Various synthetic disk plugs have been proposed in the past, but all have the problem of not conforming to the shape of the disk space. There has long been a need for a disk plug capable of supporting the disk space after a simple diskectomy.